Aluminum smelter including cells with cathode output at the bottom of the pot shell and cell stabilizing means

ABSTRACT

Aluminum smelter comprising: (i) a series of electrolytic cells, comprising an anode, a cathode and a pot shell equipped with a side wall and a bottom, each cathode including at least one cathode output, (ii) a main electric circuit through which an electrolysis current passes, including an electrical conductor connected to each cathode output of a cell N, and to the anode of a cell N+1, and (iii) a means to stabilize the electrolytic cells. At least one of the cathode outputs of the cathode of N passes through the bottom of the pot shell, and during the operation of N and N+1, the electrolysis current passes, in an upstream-downstream direction only, through each electrical conductor extending from each cathode output of N in the direction of N+1.

The present invention relates to a plant for producing aluminum by theelectrolysis of alumina, also referred to as an aluminum smelter.

The practice is known of producing aluminum industrially by theelectrolysis of alumina using the Hall-Heroult process. To this end, anelectrolytic cell is used, notably made up of a steel pot shell, aninterior refractory coating, and a cathode made of carbonaceousmaterial, connected to conductors which deliver the electrolysiscurrent. The electrolytic cell also contains an electrolytic bathnotably made up of cryolite in which the alumina is dissolved. TheHall-Heroult process consists of partially immersing a carbon block,forming the anode, into the electrolytic bath, the anode being consumedas the reaction proceeds. The liquid aluminum, produced by theelectrolysis reaction, is deposited in the bottom of the cell bygravity, forming a pad of liquid aluminum that completely covers thecathode.

Generally speaking, aluminum production plants have several hundreds ofelectrolytic cells connected in series in production halls. Anelectrolysis current, in the order of several hundreds of amperes,passes through these electrolytic cells creating significant magneticfields. Depending on the distribution of the various components of themagnetic field in the cell, the pad of aluminum may be unstable, whichsignificantly downgrades the productivity of the cell. It is notablyknown that the vertical composite of the magnetic field is a determiningfactor in the stability of an electrolytic cell.

It is known that the stability of electrolytic cells can be improved byminimizing the vertical component of the magnetic field in the cell. Todo this, the vertical component of the magnetic field relative to anelectrolytic cell is compensated owing to a special arrangement of theconductors conveying the electrolysis current from a cell N to a cellN+1. Part of these conductors, generally aluminum bars, circumvent theends of the cell N. FIG. 1 is a schematic top view of an electrolyticcell 100 wherein the magnetic field is self-compensated owing to thelayout of the conductors 101 connecting this cell N 100 to the next cellN+1 102 placed downstream. To this end, it is noted that conductors 101are off-center in relation to the cell 100 and circumvent it. Such amagnetic self-compensation method is notably known from patent documentFR2469475.

However, the self-compensation method of an electrolytic cell creates asignificant amount of design constraints owing to its large size due tothe specific arrangement of the conductors. In addition, the significantlength of the conductors needed to implement this solution generatespower loss online and requires a lot of material (aluminum conductors),hence high costs in terms of energy consumption and manufacturing.

Another cause of instability of the electrolytic cells, in addition tothe vertical component of the magnetic field, is the presence ofhorizontal electric currents in the pad of aluminum. FIG. 2 shows anelectrolytic cell 200 belonging to the state of the art, through whichan electrolysis current I₂₀₀ passes. The electrolytic cell 200 has ananode 201, a pot shell 202 notably containing an electrolytic bath 203,a pad of liquid aluminum 204 and a cathode 205. It should be noted thatthere are significant horizontal currents in the particularly conductiveareas. This is notably the case when the electrolysis current I₂₀₀passes through the pad of liquid aluminum 204.

The present invention therefore aims to remedy all or part of thesedrawbacks, by providing an aluminum smelter in which the stability ofthe liquids contained in the electrolytic cells is improved, and havinglower design, construction and operating costs.

In relation thereto, the subject of the present invention is an aluminumsmelter comprising:

(i) a series of electrolytic cells, designed for the production ofaluminum according to the Hall-Heroult process,

each electrolytic cell comprising at least one anode, a cathode and apot shell provided with a side wall and a bottom, each cathodecomprising at least one cathode output,

(ii) a main electric circuit through which electrolysis current passes,electrically connecting the electrolytic cells together,

the electrolysis current initially passing through an electrolytic cellN, placed upstream, and secondly through an electrolytic cell N+1,placed downstream,

said main electric circuit comprising an electrical conductor connectedto each cathode output of the electrolytic cell N,

the electrical conductor also being connected to at least one anode ofthe electrolytic cell N+1, in order to conduct the electrolysis currentfrom electrolytic cell N to electrolytic cell N+1,

characterized in that the aluminum smelter further comprises

(iii) at least a means to stabilize the electrolytic cells among atleast one secondary electric circuit through which an electric currentpasses, so as to compensate the magnetic field created by theelectrolysis current, or the use of a cathode with a grooved surface,

and such that

at least one of the cathode outputs of the cathode of the electrolyticcell N passes through the bottom of the pot shell,

during the operation of the electrolytic cells N, N+1 (2), theelectrolysis current (I₁) passes, in an upstream-downstream directiononly, through each electrical conductor extending from each cathodeoutput of the electrolytic cell N in the direction of the electrolyticcell N+1.

The invention therefore makes it possible to improve the stability ofthe electrolytic cells in the aluminum smelter, by acting on thehorizontal currents passing though the cells and on the magnetic fieldgenerated by the electrolysis current and/or the kinetic stability ofthe pad of aluminum contained in the cells. It simultaneously allows theconductors conveying the electrolysis current from one cell to anotherto be reduced in size and weight, and consequently reduces the costsassociated with the design and manufacture of the aluminum smelteraccording to the invention. Energy loss is further reduced.

According to another characteristic of the aluminum smelter according tothe invention, the electrolytic cells are aligned along an axis, andsuch that the electrical conductor extends in a substantiallyrectilinear manner and in a manner substantially parallel to the axis ofalignment of the electrolytic cells.

According to another characteristic of the aluminum smelter according tothe invention, each cathode further comprises at least one cathodeoutput passing through the downstream side wall of the pot shell.

This characteristic has the advantage of further reducing the size andweight of the electrical conductors conveying the electrolysis currentfrom one cell to another. This cathode output passes through the sidewall of the pot shell of the cell N on its downstream side, in order torespect the characteristic according to which each electrical conductorextends in the direction of the cell N+1, in the upstream-downstreamdirection only. Owing to the proximity of the downstream side of thecell N and cell N+1, the length of the electrical conductor connectingthis cathode output to the anode of the cell N+1 is less than that of anelectrical conductor connecting a cathode output by the bottom of thecell N to the anode of the cell N+1. This embodiment therefore has theadvantage of reducing the size and length of the electrical conductorsin relation to an embodiment of the aluminum smelter according to theinvention in which the cells comprise cathode outputs located only onthe bottom.

Preferably, each downstream cathode output passing though the side wallof the pot shell of the electrolytic cell N comprises a metal bar, moreparticularly made of steel, with a copper insert or plate.

This allows the voltage at the cathode output passing through the bottomof the pot shell to be balanced in relation to that at the level of thecathode output passing through the side wall of the pot shell.

Advantageously, the pot shell of the electrolytic cell N comprisesseveral arches secured to the side wall and to the bottom of the potshell, the electrical conductors connected to each cathode outputpassing through the bottom of the pot shell of the electrolytic cell Nextending between the arches.

This characteristic has the advantage of reducing the size of theelectrical conductors conveying the electrolysis current from one cellto another.

Advantageously, the electrolytic cells include short-circuiting means.

The short-circuiting means allow an electrolytic cell to be shortcircuited so that it can be removed for maintenance, while the othercells in the series continue to operate.

Advantageously, the short-circuiting means of the electrolytic cell N+1comprise at least a short-circuiting electrical conductor placedpermanently between electrolytic cell N and electrolytic cell N+1, eachshort-circuiting electrical conductor being electrically connected toone of the electrical conductors connected to a cathode output of thecell passing through the bottom of the shell of the electrolytic cellN+1, and each short-circuiting electrical conductor being located ashort distance from one of the electrical conductors connected to one ofthe cathode outputs of the electrolytic cell N.

According to another characteristic of the aluminum smelter according tothe invention, the short-circuiting means of the electrolytic cell N+1comprise at least a short-circuiting electrical conductor placedpermanently between electrolytic cell N and electrolytic cell N+1, eachshort-circuiting electrical conductor being electrically connected toone of the electrical conductors connected to a cathode output of thecell passing through the bottom of the shell of the electrolytic cell N,and each short-circuiting electrical conductor being located a shortdistance from one of the electrical conductors connected to one of thecathode outputs of the electrolytic cell N+1.

The short distance between the short-circuiting conductor and the otherconductor form locations for the introduction of short-circuitingblocks. These short-circuiting blocks can be introduced from above orfrom below in the second case.

Preferably, at least a secondary electric circuit includes electricalconductors running along the right side and/or the left side of theelectrolytic cells along at least one line of electrolytic cells.

Advantageously, the at least one secondary electric circuit includeselectrical conductors extending along at least one line of electrolyticcells, under said electrolytic cells.

Advantageously, the electrical conductors of the at least one secondaryelectric circuit are made of a superconducting material. This allows adecrease in the voltage drop to which each secondary circuit issubjected, thereby saving energy and enabling a less powerful and lessexpensive power substation to be used for each secondary electriccircuit. This characteristic also allows material costs to be reduced inrelation to aluminum or copper conductors. It allows the size of theelectrical conductors to be reduced, which saves space in the aluminumsmelter.

According to another characteristic of the aluminum smelter according tothe invention, the electrical conductor of the at least one secondaryelectric circuit runs along the electrolytic cells of the line(s) atleast two times.

This characteristic offers the possibility to reduce the strength of thecurrent passing through this secondary circuit in order to save energy.

The invention will be better understood from the detailed descriptiongiven below with reference to the accompanying drawings in which:

FIG. 1 is a schematic top view of an electrolytic cell of the state ofthe art,

FIG. 2 is a schematic view of an electrolytic cell acknowledged asbelonging to the state of the art,

FIG. 3 is a schematic top view of an aluminum smelter according to aspecific embodiment of the present invention,

FIG. 4 is a schematic view of a cell N and a cell N+1 of an aluminumsmelter according to a specific embodiment of the invention,

FIGS. 5 and 6 are cross-sections along lines I-I and II-II of FIG. 4,respectively,

FIG. 7 is a schematic view of an electrolytic cell according to theembodiment of FIG. 4,

FIG. 8 is a schematic top view of the cell N and cell N+1 of an aluminumsmelter according to a specific embodiment of FIG. 4,

FIG. 9 is a cross-sectional view along line III-III of FIG. 8,

FIG. 10 is a schematic view of a cell N and a cell N+1 of an aluminumsmelter according to another specific embodiment of the invention,

FIGS. 11 and 12 are cross-sections along lines IV-IV and V-V of FIG. 10,respectively,

FIG. 13 is a schematic top view of the cell N and the cell N+1 of analuminum smelter according to a second specific embodiment of theinvention,

FIG. 14 is a cross-section along line VI-VI of FIG. 13,

FIGS. 15 and 16 are schematic top views of an aluminum smelter 1according to specific embodiments of the invention,

FIGS. 17, 18 and 19 are schematic side views of grooved cathodes thatmay equip a cell of an aluminum smelter according to an embodiment ofthe invention,

FIG. 20 is a schematic front view of a grooved cathode block that mayequip a cell of an aluminum smelter according to an embodiment of theinvention,

FIG. 21 is a schematic top view of a grooved cathode block that mayequip a cell of an aluminum smelter according to an embodiment of theinvention.

FIG. 3 shows an aluminum smelter 1 including a plurality of electrolyticcells 2. The electrolytic cells 2 can be rectangular, for example. Theythus have two long sides 2 a corresponding to their length and two shortsides 2 b corresponding to their width.

The short sides 2 b of each cell 2 can be divided into a right side anda left side. The left side and the right side are defined in relation toan observer located at the main electric circuit 4 and looking in theoverall direction of the direction of the electrolysis current I₁.

The long sides 2 a of each cell 2 can be divided into an upstream sideand a downstream side. The upstream side corresponds to the long side 2a of a cell 2 adjacent to the preceding cell 2, i.e. that through whichthe electrolysis current I₁ passes first. The downstream sidecorresponds to the long side 2 a of a cell 2 adjacent to the next cell2, i.e. that through which the electrolysis current I₁ passes next. Moregenerally speaking, upstream and downstream are defined in relation tothe overall direction of the electrolysis current I₁.

In the example shown in FIG. 3, the cells 2 are aligned along twoparallel axes, so as to form a line F and a line F′. Each line F, F′ maycomprise, for example, a hundred or so cells 2. The lines F and F′ areconnected electrically to each other in series. The cells 2 areconnected electrically to each other in series. A series of cells 2,which may contain several files F, F′, is connected to its ends to apower substation 3. The electrolysis current I₁ passes through the cells2 one after the other, defining a main electric circuit 4.

In the embodiment of FIG. 3, the electrolytic cells 2 are arranged sothat their long sides 2 a are perpendicular to their alignment axis.

As can be seen in FIG. 3, the aluminum smelter 1 comprises two secondaryelectric circuits 5 and 6 separate from the main electric circuit 4.

Electrical currents I₂ and I₃ pass through the secondary electriccircuits 5 and 6. The strength of the electric currents I₂ and I₃ isbetween 20% and 100% of that of the strength of the electrolysis currentI₁ and preferably between 40% and 70%, and more particularly in theorder of half. The direction of flow of electrical current I₂ and I₃ isadvantageously the same as the direction of the flow of the electrolysiscurrent I₁. The secondary electric circuits 5 and 6 can both beconnected to a power substation 20 and 21 respectively, separate fromthe power substation 3, as can be seen for example in FIG. 15 or FIG.16.

The secondary electric circuits 5 and 6 are formed by electricalconductors arranged parallel to the axes of alignment of the cells 2.They run along the right and left sides of the electrolytic cells 2 ofeach line F, F′ of the series. The secondary electric circuits 5 and 6can also pass, in whole or in part, under the electrolytic cells 2.

In order to stabilize the liquids contained in the electrolytic cells 2,it is possible to use, in an alternative or complementary manner,secondary electric circuits 5 and 6, one or more cathode blocks 8 havinga grooved upper face, as can be seen in FIGS. 17 to 21. The upper faceof these cathode blocks 8 comprises at least one channel 8 a extendinglongitudinally over at least part of the length of the cathode blocks 8.When in operation, the upper surface of the grooves is covered by thepad of aluminum and the channels 8 a are thus occupied by the pad 11 ofaluminum that forms during the electrolysis reaction. The height of thealuminum pad above the upper surface of the grooves is notably between 3and 20 cm. Thus, the grooves and channels 8 a make it possible to limitthe movements of the pad of aluminum 11 during the electrolysis reactionand contribute to stability and to a better yield of the electrolyticcells 2.

Each electrolytic cell 2 can contain a plurality of cathode blocks 8placed next to each another. Instead of channels 8 a on the upper faceof one or more of these cathode blocks 8, it is possible to allow for aninclined upper face, such that the cathode blocks 8 placed next to oneanother form channels 8 b, as is represented schematically in FIG. 19.

Such cathode blocks with a grooved upper face are notably known frompatent document U.S. Pat. No. 5,683,559.

The upper face of these cathode blocks 8 having longitudinal channels 8a may also comprise a transversal central channel 8 c, extending atleast partially over the width of the cathode blocks 8. The centralchannel 8 c thus crosses the channel(s) 8 a extending at least partiallyover the length of the cathode blocks 8. In the example of FIGS. 20 and21, the cathode block 8 comprises a central channel 8 c on its upperface arranged perpendicularly to the channels 8 a extendingsubstantially parallel to the length of the cathode block 8.

Typically, as is represented on FIG. 4, an electrolytic cell 2 comprisesa metal pot shell 7 made of steel, for example. The metal pot shell 7has a side wall 7 a and a bottom 7 b. It is lined internally byrefractory materials (non visible). The electrolytic cell 2 alsocomprises a cathode formed of cathode blocks 8 made of carbonaceousmaterial and anodes 9 also made of carbonaceous material. The anodes 9are designed to be consumed as the electrolysis reaction progresses inan electrolytic bath 13 notably comprising cryolite and alumina. Theanodes 9 are connected to a load bearing structure by rods 10. A pad ofliquid aluminum 11 forms during the electrolysis reaction. The cathodecomprises cathode sorties 12 passing through the pot shell 7. Thecathode outputs 12 are formed, for example, by metal bars secured tocathode blocks 8. The cathode outputs 12 are themselves connected toelectrical conductors 14 enabling the electrolysis current I₁ to beconveyed from the cathode outputs 12 of a cell N (the one on the left inFIG. 4) to the anodes 9 of a cell N+1 (the one on the right in FIG. 4).

The electrolysis current I₁ first passes through the anode 9 of cell N,then the electrolytic bath 13, the pad of liquid aluminum 11, thecathode, the cathode outputs 12 and the electrical conductors 14 thatconvey it toward the anode 9 of the next cell N+1.

As is represented in FIG. 4, which illustrates a particular embodimentof the present invention, the cathode outputs 12 advantageously passthrough the bottom 7 b of the pot shell 7. This allows the horizontalelectric currents to be reduced to improve the yield of the cells 2.Furthermore, for the same mass of steel used for the horizontal partunder the anodes of the cathode output, the overall current density isreduced and thus the voltage drop. Also, the current lines tend toextend in a substantially rectilinear manner, and thus vertically in thealuminum pad as they do naturally between the anodes and the electricalconductors. For this purpose, FIG. 7 shows the current lines passingthrough an electrolytic cell 2. It is noted that the horizontal electriccurrents, particularly in the liquid aluminum pad 11, are substantiallyreduced in relation to those in FIG. 2.

Another remarkable point is that the electrical conductors 14 extend ina rectilinear manner and parallel to the alignment axis of theelectrolytic cells 2 from the cathode outputs 12 of the cell N in thedirection of the cell N+1 so that the electrolysis current passesthrough them only in the upstream-downstream direction when theelectrolytic cells 2 N, N+1 are in operation. The upstream-downstreamdirection corresponds to the overall direction of flow of theelectrolysis current I₁. Thus, an observer located at an electrolyticcell 2 and moving in the upstream-downstream direction can only movetoward cell N+1. In particular, to reach cell N+1, this observer cannotbacktrack, even partially, in the direction of the cell N−1.

In addition, the electrical conductors 14 connected to the cathodeoutputs 12 passing through the bottom 7 b of the pot shell 7 do notextend under the full width of the pot shell 7 of the cell N; anelectrical conductor 14 does not pass completely through an electrolyticcell 2 under its pot shell 7 or on the sides. In particular, they do notpass through the plane containing the upstream side wall of the potshell 7 of the cell N.

The rectilinear extension, in the downstream direction only, parallel tothe alignment axis of the electrolytic cells 2, forms the shortestelectrical path connecting a cathode output of the cell N, passingthrough the bottom 7 b of the pot shell 7 of this cell N, up to theanode 9 of the next cell N+1. Furthermore, as stated above, theelectrolysis current I₁ passing through the cell N passes through thecathode outputs 12 then the electrical conductors 14 connected to thecathode outputs 12. The electrolysis current I₁, while passing throughthe electrical conductors 14 is conveyed in a straight line parallel tothe alignment axis of the cells 2 in the direction of the next cell N+1.This notably saves energy.

In addition, this arrangement limits the overall dimensions near theelectrolytic cells 2. It thus becomes possible to reduce thecenter-to-center distance separating two adjacent cells 2 in order toincrease the available space in the aluminum smelter 1, for example toadd two additional electrolytic cells 2 or to decrease the size of thebuildings.

Also, making use of electrical conductors 14, extending in a rectilinearmanner from one cell to another parallel to the alignment axis of thecells 2, simplifies the structure of these electrical conductors 14.Their modularity makes their fabrication more economical.

It should be noted that this specific arrangement is made possiblenotably by the existence of the first secondary electric circuit 5 andthe second secondary electric circuit 6 which compensate the effects ofthe magnetic field created by the electrolysis current I₁, or that ofthe cathode with the grooved upper surface that stabilizes the movementsof the pad of liquid aluminum 11. It is not necessary to configure theelectric conducts 14 so as to obtain self-compensation of the effects ofthis magnetic field relative to each electrolytic cell 2.

FIGS. 5 and 6 are sectional views of an electrolytic cell 2 according toan embodiment of the invention, along line I-I and line II-II of FIG. 4,respectively. It can be seen that the pot shell 7 of a cell 2 issupported by a plurality of arches 15. The arches 15 are placed aroundthe pot shell 7. The arches 15 are secured against the side wall 7 a andthe bottom 7 b of the pot shell 7. They are arranged parallel inrelation to each other. A space, bounded between two consecutive arches15, is advantageously occupied by the electrical conductors 14. It willbe noted that the electrical conductors 14 can connect the cathodeoutputs 12 in pairs.

FIG. 8 is a schematic view of the top of a cell N (to the left in FIG.8), placed upstream, and a cell N+1 (to the right in FIG. 8), placeddownstream, according to the embodiment of FIG. 4. FIG. 9 is a sectionalview along line III-III of FIG. 8. The secondary electric circuits 5 and6, arranged parallel to the short side 2 b of the electrolytic cells 2,are visible. The electrical conductors 14 will also be noted, under thepot shell 7, which extend in a straight line in the direction of thecell N+1. The arches 15 are noted, mounted on the side wall 7 b of thepot shell 7 of the cell N and between which the electrical conductors 14extend. The cathode outputs 12 can be aligned according to an axisparallel to the long sides 2 a of the electrolytic cell 2, as isrepresented as dashed lines in FIG. 8.

FIG. 10 schematically represents another embodiment of an aluminumsmelter 1 according to the present invention. FIGS. 11 and 12 representa sectional view along lines IV-IV and V-V of FIG. 10, respectively. Inthis embodiment, the electrolytic cells 2 have first cathode outputs 12passing through the bottom 7 b of the pot shell 7, while the secondcathode outputs 12, located downstream from the first cathode outputs12, pass through the downstream side wall 7 a of the pot shell 7. Theelectrolytic cells 2 of the aluminum smelter 1 according to this secondembodiment thus have “mixed” cathode outputs 12, as they pass throughthe bottom 7 b and the side wall 7 a.

This arrangement allows further savings to be made in terms of material,owing to the decreased length, and thus the weight, of the electricalconductors 14.

Advantageously, the second cathode outputs 12 passing through the sidewall 7 a can include an element made of a material that conductselectricity better, such as steel, notably copper, in the form of aplate 16 or an insert, for example. The copper plate 16 placed on asteel bar allows, by its high electrical conductivity, to rebalance thevoltages on the first cathode outputs 12, passing through the bottom 7b, and the second cathode outputs 12, passing through the side wall 7 a,and thus to limit the horizontal electrical currents in the aluminumpad.

FIG. 13 schematically shows the top of a cell N, placed upstream (on theleft in FIG. 13), and cell N+1, placed downstream (on the right in FIG.13), of an aluminum smelter 1 according to the embodiment presented inFIG. 10. FIG. 14 is a sectional view along line VI-VI of FIG. 13. As inthe embodiment presented in FIG. 4, the electrical conductors 14 extendbetween the arches 15. In addition, they extend in a rectilinear mannerand the electrolysis current flows through them, during operation of theelectrolytic cells 2 N, N+1, only in the direction of the cell N+1located downstream of the cell N, from the cathode outputs 12 passingthrough the bottom 7 b of the shell of the cell N, in order to allow theelectrolysis current I₁ to be conveyed from the cathode outputs 12 ofcell N to the anode 9 of cell N+1.

As in the embodiment presented in FIG. 4, the secondary electriccircuits 5 and 6 are parallel to the axis of alignment of the cells 2.

The aluminum smelter 1 can also advantageously include means to shortcircuit each cell 2. These short-circuiting means can include electricalshort-circuiting conductors 17, shown in FIGS. 4, 8, 10 and 13. Theelectrical short-circuiting conductors 17 are arranged between twosuccessive electrolytic cells 2. In FIGS. 4, 8, 10 and 13, theelectrical conductors 17 are placed in contact with the electricalconductors 14 connected to the cathode outputs 12 passing through thebottom 7 b of the pot shell 7 of the cell N+1, and at a distance fromelectrical conductors 14 connected to the cathode outputs 12 of the cellN, so that a narrow space separates the electrical short-circuitingconductors 17 of the electrical conductors 14 connected to the cathodeoutputs 12 of the cell N, as is notably shown in FIG. 10.

The electrical short-circuiting conductors 17 are designed to shortcircuit a cell N+1, for example in order to remove the latter formaintenance. The distance between the electrical short-circuitingconductors 17 and the electrical conductors 14 connected to the cathodeoutputs 12 of the cell N is thus filled by a block made of a conductingelement (not represented) so as to conduct the electrolysis current I₁from the cell N to the cell N+2 via this block, the electricalshort-circuiting conductors 17 and the electrical conductors 14 normallyplaced under the cell N+1 (i.e. the electrical conductors 14 connectedto the cathode outputs 12 passing through the bottom 7 b of the shell 7of the cell N+1 when it is in place).

It is also possible to allow for electrical short-circuiting conductors17 placed in contact with electrical conductors 14 connected to thecathode outputs 12 of the cell N and at a distance from electricalconductors 14 connected to the cathode outputs 12 of the cell N+1passing through the bottom 7 a of the pot shell 7.

The electrical short-circuiting conductors 17 may be made of aluminum.Given that the electrolysis current I₁ passes through them onlyoccasionally during short-circuiting (for maintenance of a cell 2, or atintervals of several years), they can be designed to work at the highestallowable current density, which allows their mass to be limited.

Finally, it should be noted that, advantageously, the electricalconductors forming the secondary electric circuits 5 and/or 6 can bemade of a superconducting material.

These superconducting materials can, for example, contain BiSrCaCuO,YaBaCuO, known from patent applications WO2008011184, US20090247412 oreven other materials known for their superconducting properties.

The superconducting materials are used to convey current with little orno loss through the generation of heat by the Joule effect, as theirresistivity is zero when maintained below their critical temperature.

For example, a superconducting cable comprises a central copper oraluminum core, ribbons or fibers made of a superconducting material, anda cryogenic envelope. The cryogenic envelope can consist of a sleevecontaining a cooling fluid, such as liquid nitrogen for example. Thecooling fluid maintains the superconducting materials at a temperaturebelow their critical temperature, for example below 100 K (Kelvin), orbetween 4 K and 80 K.

The use of electrical conductors made of a superconducting material toform the secondary electric circuits 5 and 6 is of particular interestowing to their length, in the order of a few kilometers. The use ofelectrical conductors made of superconducting materials requires lessvoltage in relation to that required by electrical conductors made ofaluminum or copper. It is thus possible to decrease the voltage from 30V to 1 V. This represents a 75% to 99% decrease in energy consumption inrelation to electrical conductors made of aluminum. In addition, thecost of power substations 20 and 21, of the secondary electric circuit 5and the secondary electric circuit 6 respectively, is reducedaccordingly.

The electrical conductors of the secondary electric circuits 5 and 6 canbe advantageously run along a line F of electrolytic cells 2 at leasttwo times.

The small overall dimensions of the electrical conductors made of asuperconducting material in relation to electrical conductors made ofaluminum or copper (cross section up to 150 smaller than the crosssection of a copper conductor at equal intensity, and still further inrelation to an aluminum conductor) facilitates the formation of severalturns in series in the loops formed by the secondary electric circuits 5and 6.

In addition, it is possible to place the electrical conductor of acircuit inside a single cooling sleeve regardless of the number of turnsmade by this same conductor. In a given location, the sleeve can containseveral passages of the same electrical conductor made ofsuperconducting material.

The fact that the loop formed by the secondary electric circuits 5 and 6contains several turns in series allows the strength of the electricalcurrent I₂, I₃ passing through the secondary electric circuit 5 and thesecondary electric circuit 6, respectively, to be divided (as many timesas the number of turns made). The decrease in the value of this currentstrength allows energy losses due to the Joule effect to be lowered atthe junctions between the electrical conductors made of superconductingmaterial and the poles of the power substations. The decrease of theoverall current strength with the electrical conductors made ofsuperconducting material allows the power substations 20 and 21 to bereduced in size. For example, the power substation 20 or 21 of thesecondary electric circuit 5 or the secondary electric circuit 6comprising an electrical conductor made of superconducting material candeliver current in the order of 5 kA to 40 kA. This also allowsconventional off-the-shelf and thus inexpensive equipment to be used.

It should be noted that the electrical conductors made ofsuperconducting material can be placed under the electrolytic cells 2.

Thus, the aluminum smelter 1 according to the invention has a set ofcharacteristics, the combination of which contributes, by a synergyeffect, to reducing the design, construction and operating costs of thisaluminum smelter 1, and to increasing its productivity.

Naturally, the invention is in no way limited to the embodimentsdescribed above, as these embodiments are provided only as examples.Modifications remain possible, notably from the point of view of formingvarious elements or by the substitution of equivalent techniques,without deviating from the protective scope of the invention.

1. An aluminum smelter comprising: (i) a series of electrolytic cells,designed for the production of aluminum according to a Hall-Heroultprocess, each electrolytic cell comprising at least one anode, a cathodeand a pot shell provided with a side wall and a bottom, the cathodecomprising at least one cathode output; (ii) a main electric circuitthrough which electrolysis current passes, electrically connecting theelectrolytic cells together, the electrolysis current initially passingthrough an electrolytic cell N, placed upstream, and secondly through anelectrolytic cell N+1, placed downstream, said main electric circuitcomprising an electrical conductor connected to each cathode output ofthe electrolytic cell N, the electrical conductor also being connectedto at least one anode of the electrolytic cell N+1, in order to conveythe electrolysis current from electrolytic cell N to electrolytic cellN+1; and (iii) at least one means to stabilize the electrolytic cellsselected from the group consisting of at least one secondary electriccircuit through which an electric current passes, so as to compensatethe magnetic field created by the electrolysis current, and a cathodewith a grooved surface, such that at least one of the cathode outputs ofthe cathode of the electrolytic cell N passes through the bottom of thepot shell, and during operation of the electrolytic cells N and N+1, theelectrolysis current passes, in an upstream-downstream direction only,through each electrical conductor extending from each cathode output ofthe electrolytic cell N in the direction of the electrolytic cell N+1.2. The aluminum smelter according to claim 1, characterized in that theelectrolytic cells are aligned along an axis, and in that the electricalconductor extends in a substantially rectilinear manner and in a mannersubstantially parallel to the axis of alignment of the electrolyticcells.
 3. The aluminum smelter according to claim 1, wherein at leastone cathode output of each cathode passes through a downstream side wallof the pot shell.
 4. The aluminum smelter according to claim 3,characterized in that each cathode output passing through the downstreamside wall of the pot shell of the electrolytic cell N comprises a metalbar with a copper insert or plate.
 5. The aluminum smelter according toclaim 1, characterized in that the pot shell of the electrolytic cell Ncomprises several arches secured to the side wall and to the bottom ofthe pot shell, the electrical conductors connected to each cathodeoutput passing through the bottom of the pot shell of the electrolyticcell N extending between the arches.
 6. The aluminum smelter accordingto claim 1, characterized in that the electrolytic cells includeshort-circuiting means.
 7. The aluminum smelter according to claim 6,characterized in that the short-circuiting means of the electrolyticcell N+1 comprise at least a short-circuiting electrical conductorplaced permanently between electrolytic cell N and electrolytic cellN+1, each short-circuiting electrical conductor being electricallyconnected to one of the electrical conductors connected to one of thecathode outputs of the electrolytic cell passing through the bottom ofthe shell of the electrolytic cell N+1, and each short-circuitingelectrical conductor being located a short distance from the electricalconductors connected to one of the cathode outputs of the electrolyticcell N.
 8. The aluminum smelter according to claim 6, characterized inthat the short-circuiting means of the electrolytic cell N+1 comprise atleast a short-circuiting electrical conductor placed permanently betweenelectrolytic cell N and electrolytic cell N+1, each short-circuitingelectrical conductor being electrically connected to one of theelectrical conductors connected to one of the cathode outputs of theelectrolytic cell passing through the bottom of the shell of theelectrolytic cell N, and each short-circuiting electrical conductorbeing located a short distance from the electrical conductors connectedto one of the cathode outputs of the electrolytic cell N+1.
 9. Thealuminum smelter according to claim 1, characterized in that the atleast one secondary electric circuit comprises electrical conductorsrunning along at least one line of the electrolytic cells at a rightand/or left side of the electrolytic cells.
 10. The aluminum smelteraccording to claim 1, characterized in that the at least one secondaryelectric circuit comprises electrical conductors extending along atleast one line of the electrolytic cells, under said electrolytic cells.11. The aluminum smelter according to claim 9, characterized in that theelectrical conductors of the at least one secondary electric circuit aremade of a superconducting material.
 12. The aluminum smelter accordingto claim 11, characterized in that the electrical conductors of the atleast one secondary electric circuit run along the electrolytic cells orthe at least one line of the electrolytic cells at least two times. 13.The aluminum smelter according to claim 4, characterized in that themetal bar is made of steel.
 14. The aluminum smelter according to claim10, characterized in that the electrical conductors of the at least onesecondary electric circuit are made of a superconducting material. 15.The aluminum smelter according to claim 14, characterized in that theelectrical conductors of the at least one secondary electric circuit runalong the electrolytic cells or the at least one line of theelectrolytic cells at least two times.